Systems and methods for volt/var control in electric power management and automation systems

ABSTRACT

A dynamic auto-adaptive volt/VAR control includes a memory storing program code, a communications channel operatively connected to a volt/VAR device, and a processor. The processor is configured to access a database of prior system knowledge and receive real-time measurements and power system operating condition information. The processor processes the prior system knowledge and the real time measurements and operating condition information to create a set of commands for voltage and reactive power control that will result in at least one of: (a) maintaining a voltage profile at the volt/VAR device within predefined limits, or (b) reducing electrical losses through voltage optimization. The processor causes the set of commands to be sent to the volt/VAR device.

This application includes material which is subject to copyrightprotection. The copyright owner has no objection to the facsimilereproduction by anyone of the patent disclosure, as it appears in thePatent and Trademark Office files or records, but otherwise reserves allcopyright rights whatsoever.

FIELD

The present invention relates in general to the field of electric powermanagement and automation systems (EPMAS), including DistributionManagement Systems (DMS), Energy Management Systems (EMS), NetworkManagement Systems (NMS) and Distributed Energy Resource ManagementSystems (DERMS). In particular, the invention relates to systems andmethods for volt/VAR control (VVC) functions in such systems. Thisapplication also relates to the subject matter of U.S. patentapplication Ser. No. 14/480,038 filed Sep. 8, 2014, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND

Providing voltage to customers within a proper range is one of theelectric utility's fundamental tasks. VVC utilizes load/generationforecast, load allocation, a system network model, network topology,market information on energy trades, available real-timemeasurements/information, etc., to compute and control the desirablesettings of system devices that contribute towards voltage profile andreactive power. These volt/VAR devices include voltage regulators, loadtap changers, primary and secondary capacitor banks, distributionflexible AC transmission systems (DFACTS), unified power flow controls(UPFC), energy storage systems (ESS), and smart inverters with real andreactive power controls. Optimal settings are sent to the localcontrollers of VVC elements to be implemented in order to accomplish aset of desired objectives and satisfy a set of defined practicalconstraints, which are described as follows.

A basic requirement of VVC is to maintain the voltage profile at allload nodes within the acceptable limits under all loading conditions, asdefined by standards such as ANSI. ANSI C84.1 standard outlines threevoltage levels: low voltage LV (1 kV or less), medium voltage MV(greater than 1 kV and less than 100 kV), and high voltage HV (greaterthan or equal to 100 kV). Within each voltage level, two ranges ofvoltage are defined, Range A and Range B, discussed below.

Utilities are usually mandated to design and operate their system suchthat the service voltage is within a standard range. This is defined asRange A, and is utilized for normal operating conditions. A secondrange, Range B, is used for abnormal operating conditions. Range B is arelaxed limit that depends on extent, frequency, and duration. However,when the electrical system experiences voltage conditions in this range,corrective actions must commence within a reasonable time to bringvoltage level back within Range A. For low voltage level in distributionsystems, ANSI C84.1 provides boundary limits of −5% and +5% for Range Aand −8.3% and +5.8% for Range B. However, in medium voltage level, ANSIC84.1 provides boundary limits of −2.5 to +5% for Range A, and −5 to+5.8% for Range B.

Another objective of VVC is improving system efficiency and minimizinglosses through voltage optimization.

A further objective of VVC is reducing electrical demand throughconservation voltage reduction (CVR).

Other objectives of VVC are: power factor correction, enabling highpenetration of distributed generation (DG) and renewable resources,enabling islanded microgrids, satisfying distribution feeder capacitylimits, and satisfying limits on VVC device operations due to limit oftheir energy capacity, life expectancy, and maintenance costs.

Modern electric power systems (EPS) are faced with a high degree ofcomplexity and uncertainty due rising factors such as aging andconstrained infrastructure, penetration of distributed generation (DG),new loads (e.g. electric vehicles (EVs)), and rise of energy storagedevices. These factors may cause uncertain voltage profiling on feeders.As a result, conventional VVC strategies are becoming inadequate tosatisfy the voltage regulation and optimal system performance in termsof real-time adaptability with dynamic system operating conditions andtopologies.

Electrical power systems are furthermore hierarchical structures withgeneration and bulk power operations at the top, a transmission systemas the next tier, a distribution system as the next, etc. Furthermore,large distribution systems may include microgrids and non-microgridbranches. A microgrid typically includes localized groupings of loads,generation sources, and storage devices that are connected to atraditional centralized grid, or macrogrid.

Centralized control approaches for these large systems can beprohibitively complex and cumbersome to perform wide area-optimizedcontrol. Such systems tend to apply centralized control approaches basedon simple one-way communications to devices and heuristic rules, and notcoordinated amongst all tiers of the EPS. Alternatively, local controlapproaches will be far from optimal because there is no explicitcentralized coordination among different controllers/devices at thesystem level. From another perspective, VVC is but one application of anEPMAS. The infrastructure and resources required for implementing VVCshould be leveraged to provide other functionalities, such as microgridcontrols, optimal feeder configurations, and distributed energy resource(DER) management.

Optimizing an EPS across tiers and EPMAS functionalities can be aformidable task, particularly when network conditions change.Traditionally, volt/VAR devices such as voltage regulators and switchedcapacitor banks are operated as independent devices, with no directcoordination between the individual controllers. Such an approach mightbe effective for maintaining acceptable voltage and reactive power flownear the controllers, but typically does not produce optimal results forthe entire system.

Distribution feeders typically work in radial or open loop topologies.Therefore, distribution systems may experience issues with undervoltagedue to high loading on their longer feeders. Appropriate voltageregulation has great importance for improving voltage profile, reducingsystem losses, and increasing system efficiency.

Conventional distribution systems and their control strategies such asprotection coordination, volt/VAR control (VVC), and fault detection,have been designed based on unidirectional power flow, i.e., thesubstation is the only source of power. However, the insertion of DGunits into distribution systems renders this assumption invalid. As aresult, several challenges related to system operations such as voltageprofile, protection coordination, voltage flicker due to variable outputpower from renewable resources; reverse power flow, fault detection, andservice restoration have been raised.

Four control devices are typically used to control voltage and reactivepower flow in distribution systems: Load Tap Changer (LTC), SubstationCapacitor (SC), Step Voltage Regulator (SVR) and Feeder SwitchedCapacitor (FSC).

FIG. 1 illustrates the four typical volt/VAR control devices indistribution systems. In FIG. 1, 101 indicates a Distribution systemsubstation and 102 indicates a load tap changer (LTC) which is connectedat the main substation transformer to keep the secondary voltage closeto a specified value at different loading conditions. 103 indicates amedium voltage (MV) busbar. 104 indicates a MV to low voltage (LV)transformer. 105 indicates distribution system load points. 106indicates a substation capacitor (SC) which connects to the secondarybus of the substation to regulate the reactive power flow through themain transformer in order to keep the system operating at acceptablepower factor (pf). 107 indicates a feeder switched capacitor (FSC) whichconnects at different locations on feeders, to provide voltageregulation and reactive power compensation in order to improve thevoltage profile along the feeder. 108 indicates a step voltage regulator(SVR) which connects at different locations on feeders, to providevoltage regulation to improve the voltage profile along the feeder.

Previously, the VVC could be implemented using different approaches,such as local VVC, remote VVC, and Distribution-model-based VVC. Each ofthese approaches is discussed in more detail below.

Local VVC

Local, or standalone, VVC is based on locally available information.Control set-point adjustments for VVC devices are very infrequent andcan be implemented on a seasonal basis. In local VVC, each devicereceives local information from the system, and then through localdecision processes selects a control action to implement.

Usually, the LTC and voltage regulators are controlled with line dropcompensation (LDC). LDC estimates the line voltage drop (ΔV) andperforms voltage corrections based on feeder current (I_(comp)), voltage(V_(reg)), and system equivalent parameters (R_(set), X_(set)).

On the other hand, capacitor banks can be controlled by different modesof local controls, such as the following:

-   -   a. Power factor: closes the capacitor bank when the lagging        power factor is less than a defined threshold, and begins timing        to open the capacitor bank when the leading power factor is less        than a defined threshold. In general, power factor control is        not recommended. This is because if the power factor at light        load is low, this would not be an appropriate time to switch a        shunt capacitor in. Also, if the power factor during heavy load        is high and the capacitor bank does not operate, the potential        benefit of the capacitor bank will not be realized.    -   b. Current: closes the capacitor bank when the phase current is        greater than the high current threshold and begins timing to        open the capacitor bank when the phase current is less than the        low-current threshold. Current control works well if the power        factor of the load is fairly constant.    -   c. Voltage: closes the capacitor bank when the bus voltage is        outside of the thresholds and begins timing to open the        capacitor bank when the bus voltage greater than a defined        voltage inhibit threshold. Voltage controlled FSC are most        appropriate when the main role of capacitors is voltage        regulation.    -   d. Reactive power: energize capacitors banks when lagging kVAR        reactive power flow exceeds a set-point, and de-energize when        leading kVAR reactive power flow exceeds high leading kVAR        threshold. To minimize the reactive power flow, reactive power        controlled capacitors are most appropriate.    -   e. Time-based: configure the time of day to close and open the        capacitor bank. Thus, shunt capacitors are switched in and out        at a pre-determined time of day. This type of control can be        applied if the load characteristics are predictable and        consistent over long periods of time. However, this control        strategy can become inefficient when the load profile changes        daily or seasonally or if variable distributed generation is        involved.    -   f. Temperature: has a similar characteristic to time control        except that capacitor bank switching is triggered by ambient        temperature. This control type is suitable where loading has a        strong correlation with temperature.

The strengths and weaknesses of local VVC can be summarized as follows.The strengths are that it provides a low-cost, modular self-containedsystem requiring minimal operator involvement and does not rely on fieldcommunications. The weaknesses are that it lacks coordination amongvolt/VAR devices, with potential conflicting controls and operations;system operation may not be optimal under different conditions; it lacksvisibility beyond local conditions; it lacks flexibility andadaptability to respond to changing conditions such as load andgeneration levels; it does not handle high penetrations of distributedgeneration (DG) effectively; and it typically cannot override its setoperation during emergencies.

Remote VVC

In remote control, VVC devices are monitored and controlled by theutility's Supervisory Control and Data Acquisition (SCADA) system. LocalLTC and SVR controllers change their tapping and SC and FSC controllersopen and close their switches based only on commands from the SCADAsystem. Control decisions are based on predefined system rules orheuristics. An adjustable SCADA heartbeat time ensures thatcommunications remain active. The operation of these systems isprimarily based on a stored set of predetermined rules.

Remote VVC is typically handled by two independent processes, VARdispatch and volt control. VAR dispatch controls capacitor banks toimprove power factor and reduce electrical losses. Volt Control controlsLTCs and/or SVRs to keep consumer voltage magnitudes within standards.

The strengths and weaknesses of remote VVC can be summarized as follows.Its strengths are that it provides remote measurements withpredetermined rules; operations can be overridden during emergencies; ithas better scalability and coordination over local (standalone) control;and it has potential efficiency improvements over local control. Itsweaknesses are that it is typically more expensive and has greatercomplexity with communication infrastructure; operation of VAR and voltdevices are usually not coordinated (separate rules for VAR dispatch andvolt Control); system operation may not be optimal under differentconditions; it lacks flexibility and adaptability to respond to changingconditions such as load and generation levels (rules are fixed inadvance); it cannot handle high penetrations of DG effectively; and ittypically requires greater operator involvement and training.

Distribution Model-Based VVC

This control scheme aims to achieve better performance by utilizing the“as operated” distribution engineering model to solve the problem ofvolt/VAR as an optimization problem. This is typically run for 24 hoursof the day before the dispatch day (“day-ahead planning”) utilizingday-ahead load/generation forecast. Therefore, it develops and executesa coordinated optimal operating schedule for all VVC devices to achieveutility-specified objectives. The LTC, SVR, SC and FSC are remotelydispatched every hour, by using an automated schedule, which is definedbased on day-ahead load/generation forecast.

An objective of the volt/VAR optimization problem is to minimize systemlosses, while keeping consumer voltage magnitudes within standards andlimiting the number of LTC, SVR and capacitor banks switchingoperations. Solving this optimization problem is not a trivial taskbecause of the load variation, the discrete nature of the LTC, SVR andcapacitor bank switching and nonlinear power flow equations.

The strengths and weaknesses of distribution model based VVC can besummarized as follows. The strengths are that it provides a coordinatedsystem of VVC devices; it can provide an optimal solution based onday-ahead load forecasting; it provides flexible operating objectivesaccommodating various needs; it is able to handle complex feederarrangements; it can model the effects of DG and other modern gridelements such as active inverter controls and electric vehicles; it ishighly scalable; and the system can assist the operator with trainingand automated operations. Its weaknesses are that its complexity leadsto a lack of field proven products except in centralized distributionmanagement systems; it has a higher cost to implement, operate andsustain; due to load variations, while VVC settings are optimum duringtheir dispatching times, there is no guarantee that they will continueto be optimal until the next scheduled dispatch; it does not typicallyhave the capability to adapt automatically to load changes that deviatefrom forecast.

Inappropriate voltage regulation can cause many problems for customers.These include unsafe and inefficient operation of electronic devices,tripping of sensitive loads, overheating of induction motors (IMs), andequipment failures that lead to higher no-load losses in transformers.Additionally, inappropriate control of reactive power flow can increasethe total system losses.

For example, the continuous increase of renewable DG penetration changesthe characteristics of distribution systems from being passive withunidirectional power flow to active with bidirectional power flow. TheseDGs are usually not utility owned and are intermittent energy sourcessuch as wind and solar based DG units. When DGs are connected to adistribution system, they alter the voltage profile and interfere withthe conventional VVC strategies of LTCB, SVRs and capacitor banks.Consequently, overvoltage, undervoltage, increased system losses andexcessive wear and tear of VVC devices may occur. In addition, loadvariations are becoming more adverse, with EVs on the rise and changesin usage by end-use customers through demand response programs. High R/Xratio for distribution lines limits the voltage correcting abilities ofVAR-only devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments as illustrated in the accompanyingdrawings, in which reference characters refer to the same partsthroughout the various views. The drawings are not necessarily to scale,emphasis instead being placed upon illustrating principles of theinvention.

FIG. 1 shows a schematic block diagram illustrating typical Volt/VARcontrol devices in distribution systems.

FIG. 2 shows a block diagram illustrating a multi-tier voltage andreactive power control methodology in accordance with an embodiment.

FIG. 3 shows a block diagram illustrating a multi-stage voltage andreactive power control methodology in accordance with an embodiment.

DETAILED DESCRIPTION

To mitigate existing volt/VAR control limitations and facilitate aseamless operation of modern distribution systems, a dynamic optimalvolt/VAR control system and method is provided, with the followingobjectives:

-   -   a. Consider the interaction of the new system elements such as        DG units, energy storage devices, electric vehicle chargers,        UPFCs DFACTS, and demand response programs, in the DOVVC        process.    -   b. Minimize the system losses, maximize grid efficiency, improve        asset utilization, improve power factor, while limiting the        number of volt/VAR device operations and keeping consumer        voltage magnitudes within standards    -   c. Dynamic model updates and automatic volt/VAR device        set-points upon:        -   i. Regular time intervals (e.g. hourly)        -   ii. Distribution network reconfiguration        -   iii. Change in load demand compared to the forecasted load        -   iv. Change in generation compared to the forecasted            generation        -   v. Violation of operational constraints, such as due to            bidirectional power flow from DGs (e.g. reverse power flow,            load/generation unbalance) or any emergency situation (e.g.            feeder fault)    -   d. Manage and coordinate multiple objectives and constraints        from multiple EPS tiers.

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The following description and drawings are illustrative andare not to be construed as limiting. Numerous specific details aredescribed to provide a thorough understanding. However, in certaininstances, well-known or conventional details are not described in orderto avoid obscuring the description. References to one or an embodimentin the present disclosure are not necessarily references to the sameembodiment; and, such references mean at least one.

Reference in this specification to “an embodiment” or “the embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least an embodimentof the disclosure. The appearances of the phrase “in an embodiment” invarious places in the specification are not necessarily all referring tothe same embodiment, nor are separate or alternative embodimentsmutually exclusive of other embodiments. Moreover, various features aredescribed which may be exhibited by some embodiments and not by others.Similarly, various requirements are described which may be requirementsfor some embodiments but not other embodiments.

The present invention is described below with reference to blockdiagrams and operational illustrations of methods and devices forvolt/VAR control in electric power management and automation systems. Itis understood that each block of the block diagrams or operationalillustrations, and combinations of blocks in the block diagrams oroperational illustrations, may be implemented by means of analog ordigital hardware and computer program instructions. These computerprogram instructions may be stored on computer-readable media andprovided to a processor of a general purpose computer, special purposecomputer, ASIC, or other programmable data processing apparatus, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, implements thefunctions/acts specified in the block diagrams or operational block orblocks. In some alternate implementations, the functions/acts noted inthe blocks may occur out of the order noted in the operationalillustrations. For example, two blocks shown in succession may in factbe executed substantially concurrently or the blocks may sometimes beexecuted in the reverse order, depending upon the functionality/actsinvolved.

The nature of distribution systems is normally dynamic due to changes intheir load conditions and more recently, renewable resources generationwhich brings uncertainty and randomness to power system operations. TheVVC problem is one of the most challenging problems in distributionsystem operation. Previously, there was no general optimizationtechnique to be used by all utilities to find a high-quality solution tosatisfy all requirements. For example, exhaustive search is inefficientto meet fast control requirement due to its time consuming calculations.Furthermore, traditional knowledge-based techniques such as expertsystems, fuzzy logic, and heuristic rules cannot optimally adjust/updatetheir control decisions due to variation of operational points.

In an embodiment, the presently disclosed system and method can providea novel and reliable solution to the VVC problem. In order to alleviatethe limitations of the previous methods and to provide an efficient andadaptive system operation, the system knowledge together with an onlinecontrol can be used, as discussed below.

The VVC algorithm search efficiency is improved and sped up when theproblem search space is reduced by prior system experience. Offlinesearch for different time frames ahead (i.e., seasonal, weekly, anddaily) and/or historical system information can be used from this priorsystem knowledge.

This knowledge is accumulated in a database and optimized by optimalsearch.

By finding the different combinations of operation options in advance,the optimal combination that satisfies the desired flexible objectivescan be found. For example, the optimal combination can be selected tominimize the operational cost due to: energy losses, generationcurtailment, reactive power, ancillary services, load shedding, andenergy storage.

In an embodiment, the presently disclosed methods can provide multi-tiermulti-stage voltage and reactive power control (VVC) in EPMASimplementation. These methods can be divided into: (1) multi-tiervoltage and reactive power control; and (2) multi-stage voltage andreactive power control. These methods are to be embedded in the EPMASand are described in the following sections.

Multi-Tier Voltage and Reactive Power Control

The multi-tier voltage and reactive power control is based on thehierarchal structure of electrical power systems which have multi-tiercontrol with independent system operator (ISO) at the top (Player 1) andassumed to include the independent market operator (IMO), transmissioncompany as the next tier (Player 2) and assumed to include anytransmission system operator and regional transmission operator,distribution company as the next (Player 3) and assumed to include anydistribution system operator and microgrid operators, and DERowners/operators, nanogrid operators and electricity users/customers(player 4). The proposed multi-tier voltage and reactive power controlis performed through these players, where each player contributes basedon its control authority and its available energy and informationresources/devices/controllers in finding the optimal set-points ofcontrol variables according to certain criterion.

In an embodiment, the presently disclosed system and method for themulti-tier voltage and reactive power control consists of severalcascaded stages. In the first stage (i.e., player 1), the set-points ofcontrol variables are determined to satisfy a criterion (M₁) of thisspecific stage. The outputs of the first stage are the optimaldevices/controllers set-points to match this stage. Then, in each stagei, where i={2, 3, 4} for each of the players, the aim is to tune thedevices/controllers set-points resulted from the previous stage. Thetuning is performed by satisfying the criterion of the current stagewhile keeping the M_(i-1) from stage i-1 as a hard constraint. Thismulti-tier control guarantees the full coordination among differentlevels of control/players to avoid contradiction in objectives.Furthermore, it provides effective way for cross optimization andappropriate use of shared resources for different system applications.

The structure of the multi-tier voltage and reactive power controlmethodology is illustrated in FIG. 2 and can be explained as follows.With reference to FIG. 2, 201 indicates Player 1 for independent systemoperators, including independent market operators. 202 indicates Dataflow from Player 2 (204) to player 1 (201). 203 indicates a data flowfrom Player 1 (201) to Player 2 (204). 204 indicates Player 2 fortransmission company, including transmission system operators andregional transmission operators. 205 indicates a Data flow from Player 3(207) to Player 2 (204). 206 indicates a data flow from Player 2 (204)to Player 3 (207). 207 indicates Player 3 for distribution company,including distribution system operators and microgrid operators. 208indicates a Data flow from player 4 (210) to player 3 (207). 209indicates a Data flow from Player 3 (207) to Player 4 (210). 210indicates Player 4 for DER owners/operators, nanogrid operators andelectricity users/customers. 211 indicates a data flow from hardwarelayer (211) to player 4 (210). 212 indicates a data flow from player 4(210) to hardware layer (211).

In FIG. 2, 213 indicates the hardware layer for electric power system,which has the following components: 213 a indicates substations; 213 bindicates sensors and meters; 213 c indicates capacitors, load tapchangers (LTCs), and step voltage regulators (SVRs); 213 d indicatesFACTs and DFACTs; 213 e indicates switches; 213 f indicates loads; and213 g indicates generation.

With continued reference to FIG. 2, 214 indicates data flow from coreanalytics engine (216) to hardware layer (213). 215 indicates Data flowfrom hardware layer (213) to core analytics engine (216). 216 indicatesCore analytics engine, which includes the following sub-components: 216a indicates system modeling; 216 b indicates topology processor; 216 cindicates load and generation forecasting; 216 d indicates loadallocation; 216 e indicates state estimation; 216 f indicates powerflow; 216 g indicates an optimizer.

In FIG. 2, 217 indicates data flow from application engine (219) to coreanalytics engine (216). 218 indicates data flow from core analyticsengine (216) to application engine (219). 219 indicates applicationengine, including the following sub-components: 219 a indicates volt/VARcontrol; 219 b indicates fault location, isolation and servicerestoration (FLISR); 219 c indicates loss minimization; 219 d indicatescost minimization; 219 e indicates Distributed Generation (DG)penetration maximization; 219 f indicates Electric Vehicles (EV)penetration maximization; 219 g indicates optimization assetutilization.

With continued reference to FIG. 2, data flow 220 from applicationengine (219) to updated set-points or control decisions (221)implemented on the volt/VAR devices can be provided by network adaptersassociated with various components of the system, including componentsof the EPMAS and the volt/VAR devices themselves. Other communicationschannels, such as serial and parallel communications, may be utilized toprovide such communications. 221 indicates updated set-points or controldecisions. 222 indicates data flow from control decisions (221) tohardware layer (213).

Multi-Stage Voltage and Reactive Power Control

In an embodiment, the invention utilizes a multi-stage volt/VAR controlalgorithm to facilitate the modern distribution system practicalimplementation. This method can be divided into two types of stages:

Offline stages (Stage 0-2) to determine dispatch schedule based onforecasted load and generation. This useful control knowledge is savedin database memory to facilitate full operating control. Also, theircontrol decisions can be implemented as a backup for online stage incase of its failure.

Online stage (Stage 3) to determine the optimal real time instantaneousoperation of VVC devices, based on available knowledge and online searchtechnique. Furthermore, it gradually acquired control knowledge andsaved in database memory for further applications.

The structure of the multi-stage voltage and reactive power controlmethodology is illustrated in FIG. 3 and can be explained as follows.301 indicates stage 0 for seasonal or annual planning and configuration.302 indicates Control variables and system components status flow fromstage 0 (301) to database (303). 303 indicates a database including allsystem parameters, control variables, forecasted load and generation,allocated load, etc. 304 indicates data flow from database (303) to coreanalytics engine (216). 305 indicates Data flow from database (303) todefine stages prioritization model (306). 306 indicates a userpreference model to define stages prioritization based on device type,location, economics and policy. 306 a indicates VVC devicesoptimization; 306 b indicates DG VAR optimization; 306 c indicatescontrollable loads (CLs) VAR optimization; 306 d indicates DG activepower control and load shedding.

With continued reference to FIG. 3, 307 indicates Data flow from userpreference model to define stages prioritization (306) to stage 1 forweek ahead scheduler (309); 308 indicates week ahead data flow fromdatabase (303) to stage 1 for week ahead scheduler (309); 309 indicatesStage 1 for week ahead scheduler: 309 a indicates Stage 1.1 (Highestpriority stage); 309 b indicates data flow from stage 1.1 (309 a) tostage 1.2 (309 c); 309 c indicates Stage 1.2; 309 d indicates data flowfrom stage 1.2 (309 c) to stage 1.3 (309 e); 309 e indicates Stage 1.3;309 f indicates data flow from stage 1.3 (309 e) to stage 1.4 (309 g);and 309 g indicates Stage 1.4 (Lowest priority stage).

310 indicates data flow from stage 1 for week ahead scheduler (309) tostage 2 for day ahead scheduler (312). 311 indicates day ahead data flowfrom database (303) to stage 2 for day ahead scheduler (312). 312indicates Stage 2 for day ahead scheduler. 313 indicates data flow fromstage 2 for day ahead scheduler (312) to stage 3 for online control(315). 314 indicates real-time data flow from database (303) to stage 3for online control (315). 315 indicates stage 3 for online control. 316indicates data flow from stage 3 (315) to the distribution network(213). 317 indicates data flow from FLISR application (219 b) to thedistribution network (213). 318 indicates data flow from optimizationasset utilization application (219 g) to the distribution network (213).319 indicates data flow from the distribution network (213) to database(303).

Stage 0 (301): Planning and Configuration

This stage can be applied pre-installation during planning andengineering, or can be performed seasonally and yearly. It aims toconfigure and plan system operations with respect to volt/VAR devicelocations and sizing, multi-tier objectives, load variation, DGsavailability, margins of switching actions, system operational limits,different possibilities of operation, and status of distributionbreakers, switches, reclosers, fuses, jumpers, line cuts, etc.

Stage 1 (309): Week-Ahead Scheduling

To achieve fast and efficient online response, full control knowledgeshould be readily stored in database and prepared for use. By using thepredicted load and generation of renewable-based DGs for week-ahead andother important factors (e.g. historical network data such as historicalload profile, DG output power generation, and corresponding implementedvolt/VAR devices control decisions), a week-ahead schedule can beplanned for the system for all possible future load/generationcombinations.

Multiple objectives can be considered from multiple EPS tiers, withoffline week-ahead optimization providing the database with a set ofoptimal tradeoff solutions. Each solution will have a major improvementin one of the objectives and has its unique contribution to meet otherobjectives. Selecting a proper solution from this set will be flexibleand mainly depend on each utility's control preference. For the sake ofreliable operation, this stage is considered as a guide for stage 2 aswell as a backup in case of failure (e.g. extended loss ofcommunication).

Stage 2 (312): 24 hr Day-Ahead Scheduling

In order to realize the full control information and to update thecontrol decisions of stages 0 and 1, the day-ahead scheduler defines theVVC devices set points at each dispatch time interval of the day byusing the day-ahead forecasts of electrical loads as well as DGproductions. The inputs include multi-tier objectives, electrical loadforecasts, forecast of energy supplied by DG units, and constraints(upper and lower limits) relevant to the technical system operation.This stage is considered as a guide for stage 3 as well as a backup incase of failure.

Stage 3 (315): Online Dispatch Control

The operating points may change with time compared to the forecastedones due to the uncertain and dynamic nature of distribution systems. Tofollow these changes and to meet the varying control preferences, onlinedispatch control will be applied. The online control stage processes thereal-time distribution system measurements and requests from multipleEPS tiers to determine appropriate volt/VAR control actions and provideclosed-loop feedback to accomplish electric utility specifiedobjectives.

To provide an efficient online feasible solution within a limited timeinterval, the prepared control knowledge from offline stages areincluded. Therefore, to reflect the distribution network conditions ateach dispatch time interval, the day-ahead decisions from Stage 2 areadjusted based on the difference between the measured and forecastedloads. Stage 3 determines whether to follow the control sequence whichis assigned by the day-ahead schedule or to run an optimizationprocedure in order to modify/update the volt/VAR control decisions thatwere assigned by the day-ahead schedule.

In an embodiment, the online control algorithm can be implemented withfour steps or phases. The first is to collect real-time data of thenetwork state in terms of volt/VAR devices set-points and measurementpoints, and collect the adjusted forecasts of both DG mean productionand load requests, from multiple EPS tiers. The second is to run thepower flow based on the day-ahead scheduler settings/decisions. Then, ifany technical constraint is violated (e.g. the voltages values deviatefrom the acceptable limits), an optimization procedure starts whichmodifies the decisions that were assigned by the day-ahead scheduler.Finally, if there is no constraints violation, the day-ahead scheduleroptimal decisions are maintained (no corrective action taken).

User Preference Model to Define Stages Prioritization (306)

Four sub-stages are embedded within each Stage X, where X=1, 2, and 3.The four stages aim to find appropriate setting of the volt/VAR devicesset-points in order to maintain the voltage profile within the limitsand to achieve the desired objectives. The defined stages prioritizationis based on device type, location, economics and policy. Thus, thesequence of these four volt/VAR control stages is completely dependingon each utility policy, regulations (e.g., the allowed number ofswitching actions for each device, cost of switching actions, and itsevaluation of the expected benefits compared to switching consequencesand devices to be used) and the available volt/VAR compensation devicesin its distribution network.

The following section gives an example of these stages sequence thatfocuses on the volt/VAR control capability of different availabledevices and their contribution in maintaining the voltage profile withinthe standard limits.

VVC Devices Optimization (306 a)

This stage represents the first defense line for volt/VAR controlproblem. VVC devices such as step voltage regulators, load-tap changingtransformers, and switched and fixed capacitor banks aim to keepcustomer voltages within regulatory bandwidths, free up capacity in thegeneration, transmission, and distribution systems, and reduce realpower losses.

In the market of active distribution networks, FACTS can operate inmedium and low voltage levels with major objectives of improving voltageprofiles, correcting power factor, and reducing line losses. DFACTSdevices offer a flexible and comprehensive solution to voltage profilecontrol in distribution systems. The combination of fixed and switchedcapacitors may bring variable reactive power, but it falls short toprovide the exact requirement. In addition, capacitors with inductivecomponents for solving the overvoltage issues may produceFerro-resonance. Thus, using DFACTS with the traditional VVC devices(LTC, SVR, SC, and FSC) overcome these limitations and makes the VVCoptimization works more efficiently. This is because DFACTS haveimproved voltage and current handling capabilities. For example, adevice such as STATCOM has the ability to provide a solution in fastresponse time which supports the dynamic voltage control requirement inthe system. On the other hand, a device such as static VAR compensatoris able to provide voltage control within very tight parameters despitea widely varying load and/or output from DGs.

The optimum settings of VVC devices (e.g. LTC, SVR, SC, FSC, and DFACTS)depend on the following: the spatial distribution of load (where on thefeeder, e.g. load allocation); the phase connection of load (whichphase); the load characteristics with respect to voltage (constantpower, constant current, constant impedance, and percent mix); networktopology and parameters; transformer parameters and connection types(delta or wye-connected); and variations of load and/or DG output power.

VVC devices optimization uses bidirectional balanced/unbalanced powerflow, load/generation forecast (LGF), load allocation (LA), and systemmodeling applications to obtain the optimal network state. It estimatessensitivity/gradient factors in order to obtain intermediate solutionsin the voltage control iterations. Then, it checks the feasibility ofcandidate solutions to be implemented. One of the major applications ofeffective VVC is the implementation of conservation voltage reduction(CVR). CVR provides demand reduction through controlled reduction inoperating voltage at customer load points.

The outputs of the VVC devices optimization can include the optimalvoltage regulator tap settings, on-load tap changer (OLTC) tap settings,capacitor banks switching, and DFACTS settings. These optimal settingsare sent to their corresponding local controllers to be implemented inorder to accomplish the desired objectives.

DG VAR Optimization (306 b)

The connection of a DG unit modifies the voltage profile on distributionfeeders due to their injected active and/or reactive power in thedistribution network. Usually voltage increases at DG connection pointsand on the entire feeder. Furthermore, DGs connection effects ondistribution feeders' voltage profile can be summarized as follows: DGconnection may cause overvoltage during minimum load times; DGs mayun-optimise (i.e. cause improper decisions) VVC devices settings,especially when DGs are not allocated homogeneously among differentfeeders; and, with high DG penetration, excessive wear and tear for VVCdevices, unaccepted voltage fluctuations, voltage unbalance and changein the system losses are expected.

The operating mode of each DG unit can furthermore have one of twostates, normal state or disturbed state. In the normal state, there thevoltage is located inside the desired operating band such as voltage(i.e. V_(min)≦V≦V_(max)), frequency, and unbalance. In this case, DGoperates in P/Q mode where DGs inject fixed active power based on theirrating.

In the disturbed state, where voltage violates the desired operatinglimits (e.g. V<V_(min) or V>V_(max)). In this case, the goal of each DGcontroller is to maintain the operating point inside the desiredoperating band. DG can then operate in voltage regulation mode (AVR forsynchronous machines and P/V mode for inverter based DGs), and onlyreactive power is used to control voltage at DG point of common coupling(PCC). This stage includes consideration of all VVC elements in theprevious stage as well as the DG voltage set points that bring thesystem voltage profile within the desired limits. In this case, the DGtechnical limits play an important role in their contributions to thevoltage control problem. The contribution of each DG depends on itsreactive power limitation (Q_(min) and Q_(max)). Hence, if it cannotreturn the desired voltage range within its reactive power limitation,the voltage may change to reach a critical state.

Thus, an upgrading for the conventional voltage and reactive powercontrol techniques from their passive form to an active control isdesireable. DG VAR optimization stage refers to actions that are neededto bring the system under satisfactory limits because VVC devicesoptimization stage actions are insufficient. DG VAR optimization stageprovides the participation of DGs in voltage control.

Controllable Loads (CLs) VAR Optimization (306 c)

CLs VAR optimization stage refers to actions that are needed to bringthe system under satisfactory limits because stages 306 a and 306 bactions are insufficient. Stage 306 c provides the participation ofcontrollable loads in voltage control through controlling their reactivepower requirements. Stage 306 c includes consideration of VVC devices(Stage 306 a) and DG VAR (Stage 306 b).

Because loads are distributed throughout the grid, their level ofspatial and temporal flexibility allows them to respond instantaneouslyto contingencies. The main concept of demand response is based oncontrolling those loads in an active manner. For example, electricvehicles (EVs) are emerging as controllable loads which their time ofcharging could be controlled. Thus, they can have a significant impacton power demand shaping. Each EV requires a charger in order to connectthe vehicle to grid. The charger AC/DC converter is capable of adjustingits reactive power in a specified range. These chargers are alwaysconnected to the grid and their reactive power capability (injected orabsorbed reactive power) depends on: the actual active power transfer ofthe AC/DC converter; the nominal kVA rating of the converter; thevoltage at the point of common coupling; converter dc link voltage; andinterfacing reactance, which includes the interfacing transformer andthe filter equivalent reactance.

Thus, when the EV is connected to the distribution network through theconverter for charging, its reactive power can be reduced to a smallamount. Furthermore, at contingencies, the AC/DC converter can supportthe grid with its reactive power.

DG Active Power Control and Load Shedding (306 d)

This stage represents the last defense line for volt/VAR controlproblem. Stage 306 d refers to urgent actions that are needed to bringthe system under satisfactory limits because stages 306 a, 306 b and 306c actions are insufficient. For example, the DG and CLs cannot act anymore by compensation of reactive power to bring the voltage within theadmissible limits. Thus, regulation of active power becomes compulsory.

Stage 306 d includes active power regulation actions in addition to thecontrol actions in Stage 306 c. The active power regulation actions caninclude load shedding, system reconfiguration (i.e., transferringsection with some load points from the overloaded/undervoltage feeder toother neighboring feeders), and/or DG generation increase (i.e., in casefor severe undervoltages) or DG generation curtailment (i.e., in casefor high overvoltage's) for consumers and/or DG owners who haveagreements with their utilities to be subjected to those emergencyactions.

The various embodiments of the invention described above can also beapplied where advanced meter infrastructure (AMI) and two-waycommunication are implemented everywhere in electrical powerdistribution systems under the concept of smart grid. For buses thathave installed meters, the load and voltage profiles will be treated asknown load and voltage values. The load profile can be forecasted withbetter accuracy which will allow the load allocation and thus volt/VARcontrol to improve the overall performance of the system operation.Furthermore, the two-way communication will facilitate the applicationof distributed control and parallel processing. In addition,communication and real-time data will enable efficient coordinationamong devices and will allow to take the market information on energytrades and prices into consideration.

Thus, the invention as described above can provide a dynamic(auto-adaptive) optimal VVC (DOVVC) for modern electric power systems.In various embodiments, the advanced DOVVC scheme can enhance overallefficiency via reducing the system losses. The described system can alsoreduce energy demand via applying conservation voltage reduction (CVR),in which the load powers are reduced through optimal reduction in thecustomer operating voltages. The systems and method can improve thevoltage profile under variable generation, storage, and demandconditions. The systems and methods described can also improveutilization of system assets, enable increased DG penetration byenhancing voltage and current profiles, improve power quality such aspower factors, and coordinate objectives and constraints betweenmultiple tiers of EPS operations.

In various embodiments, the invention can provide novel systems andmethods for volt/VAR control that are multi-stage, in that they providevoltage and reactive power control through several stages in the timedimension. Such systems and methods can also provide volt/VAR controlthat is multi-tier in that voltage and reactive power control areperformed on several tiers in control authority/players dimension. Thesesystems and methods can also be configured to accommodate all resources,i.e., to include all available devices and field information frommonitors, controllers, intelligent electronic devices, installed atdifferent system components. Such components include meters, sensors,capacitor banks, battery energy storage systems, distributed generationunits, electric vehicles chargers, switches, and substations.

In various embodiments, the invention can provide novel systems andmethods for volt/VAR control that are distributed in that they supportparallel processing, and can be centralized at one controller ordecentralized across multiple controllers. The systems and methodsdescribed above, in various embodiments, can be configured withadjustable settings to meet the requirements of a large variety of nodetypes and system configurations. These systems can further be dynamic inthat they can adjust their operations based on real-time measurementsand power system operating conditions. Such systems can be configured toprovide flexibility according to different control preferences, and canbe applied to any distribution system to provide coordination among allvolt/VAR devices, DFACTS, DGs and controllable loads.

At least some aspects disclosed can be embodied, at least in part, insoftware. That is, the techniques may be carried out in a specialpurpose or general purpose computer system or other data processingsystem in response to its processor, such as a microprocessor, executingsequences of instructions contained in a memory, such as ROM, volatileRAM, non-volatile memory, cache or a remote storage device.

Routines executed to implement the embodiments may be implemented aspart of an operating system, firmware, ROM, middleware, service deliveryplatform, SDK (Software Development Kit) component, web services, orother specific application, component, program, object, module orsequence of instructions referred to as “computer programs.” Invocationinterfaces to these routines can be exposed to a software developmentcommunity as an API (Application Programming Interface). The computerprograms typically comprise one or more instructions set at varioustimes in various memory and storage devices in a computer, and that,when read and executed by one or more processors in a computer, causethe computer to perform operations necessary to execute elementsinvolving the various aspects.

A non-transient machine-readable medium can be used to store softwareand data which when executed by a data processing system causes thesystem to perform various methods. The executable software and data maybe stored in various places including for example ROM, volatile RAM,non-volatile memory and/or cache. Portions of this software and/or datamay be stored in any one of these storage devices. Further, the data andinstructions can be obtained from centralized servers or peer-to-peernetworks. Different portions of the data and instructions can beobtained from different centralized servers and/or peer-to-peer networksat different times and in different communication sessions or in a samecommunication session. The data and instructions can be obtained inentirety prior to the execution of the applications. Alternatively,portions of the data and instructions can be obtained dynamically, justin time, when needed for execution. Thus, it is not required that thedata and instructions be on a machine-readable medium in entirety at aparticular instance of time.

Examples of computer-readable media include but are not limited torecordable and non-recordable type media such as volatile andnon-volatile memory devices, read only memory (ROM), random accessmemory (RAM), flash memory devices, floppy and other removable disks,magnetic disk storage media, optical storage media (e.g., Compact DiskRead-Only Memory (CD ROMS), Digital Versatile Disks (DVDs), etc.), amongothers.

In general, a machine readable medium includes any mechanism thatprovides (e.g., stores) information in a form accessible by a machine(e.g., a computer, network device, personal digital assistant,manufacturing tool, any device with a set of one or more processors,etc.).

In various embodiments, hardwired circuitry may be used in combinationwith software instructions to implement the techniques. Thus, thetechniques are neither limited to any specific combination of hardwarecircuitry and software nor to any particular source for the instructionsexecuted by the data processing system.

The above embodiments and preferences are illustrative of the presentinvention. It is neither necessary, nor intended for this patent tooutline or define every possible combination or embodiment. The inventorhas disclosed sufficient information to permit one skilled in the art topractice at least one embodiment of the invention. The above descriptionand drawings are merely illustrative of the present invention and thatchanges in components, structure and procedure are possible withoutdeparting from the scope of the present invention as defined in thefollowing claims. For example, elements and/or steps described aboveand/or in the following claims in a particular order may be practiced ina different order without departing from the invention. Thus, while theinvention has been particularly shown and described with reference toembodiments thereof, it will be understood by those skilled in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A multi-stage dynamic auto-adaptive volt/VARcontrol, comprising: memory storing program code; a communicationschannel operatively connected to a volt/VAR device; a processorconfigured to: access a database of prior system knowledge; receivereal-time measurements and power system operating condition information;process the prior system knowledge and the real time measurements andoperating condition information to create a set of commands for voltageand reactive power control that will result in at least one of: (a)maintaining a voltage profile at the volt/VAR device within predefinedlimits, or (b) reducing electrical losses through voltage optimization;cause the set of commands to be sent to the volt/VAR device through aplurality of stages in the time dimension.
 2. The volt/VAR controlaccording to claim 1, wherein the commands comprise updated set points.3. The volt/VAR control according to claim 1, wherein the commandscomprise control decisions.
 4. The volt/VAR control according to claim1, wherein the volt/VAR device comprises a voltage regulator.
 5. Thevolt/VAR control according to claim 1, wherein the volt/VAR devicecomprises a load tap changer.
 6. The volt/VAR control according to claim1, wherein the volt/VAR device comprises a primary or secondarycapacitor bank.
 7. The volt/VAR control according to claim 1, whereinthe volt/VAR device comprises a distribution flexible AC transmissionsystem.
 8. The volt/VAR control according to claim 1, wherein thevolt/VAR device comprises a unified power flow control.
 9. The volt/VARcontrol according to claim 1, wherein the volt/VAR device comprises anenergy storage system.
 10. The volt/VAR control according to claim 9,wherein the volt/VAR device comprises a switched capacitor bank.
 11. Thevolt/VAR control according to claim 1, wherein the volt/VAR devicecomprises a smart inverter.
 12. The volt/VAR control according to claim1, wherein the volt/VAR device comprises a device having with real andreactive power controls.
 13. The volt/VAR control according to claim 1,wherein the control is configured to support parallel processing in amanner whereby it can be centralized at one controller or decentralizedacross multiple controllers.
 14. The volt/VAR control according to claim1, wherein the volt/VAR device comprises a plurality of volt/VARdevices.
 15. A multi-tiered dynamic auto-adaptive volt/VAR control,comprising: memory storing program code; a communications channeloperatively connected to a volt/VAR device; a processor configured to:access a database of prior system knowledge; receive real-timemeasurements and power system operating condition information; processthe prior system knowledge and the real time measurements and operatingcondition information to create a set of commands for voltage andreactive power control that will result in at least one of: (a)maintaining a voltage profile at the volt/VAR device within predefinedlimits, or (b) reducing electrical losses through voltage optimization;cause the set of commands to be sent to the volt/VAR device through aplurality of tiers of a hierarchical electrical power system.
 16. Adistributed dynamic auto-adaptive volt/VAR control, comprising: memorystoring program code; a communications channel operatively connected toa volt/VAR device; a processor configured to support parallel processingin a manner whereby it can be centralized at one controller ordecentralized across multiple controllers, the processor being furtherconfigured to: access a database of prior system knowledge; receivereal-time measurements and power system operating condition information;process the prior system knowledge and the real time measurements andoperating condition information to create a set of commands for voltageand reactive power control that will result in at least one of: (a)maintaining a voltage profile at the volt/VAR device within predefinedlimits, or (b) reducing electrical losses through voltage optimization;and cause the set of commands to be sent to the volt/VAR device.